CHORDATADescription:The phylum Chordata includes three subphyla: the
Urochordata or tunicates, the Cephalochordata or lancelets, and the Vertebrata
or vertebrates. The phylum
Chordata is characterized by the presence at some stage of life of a notochord,
a dorsal hollow nerve cord, and gill slits. The notochord is a stiff dorsal rod
of cartilage that provides rigidity and protection for the dorsal nerve cord. It is present in adults of the subphylum
Cephalochordata and the fish classes Agnatha and Chondrichthyes, but is
replaced by a bony vertebral column in the other classes
of the subphylum Vertebrata. The dorsal hollow
nerve cord is present in adults of all classes
of vertebrates. All fishes and some amphibians have gill slits as adults, but
they are present only in the larvae of the other classes of vertebrates. The
vertebrates are characterized by the presence of a skull that protects the
brain and, in most classes, a cartilaginous or
bony vertebral column that protects the spinal cord.Vertebrates are
tremendously varied in body form and include fishes, amphibians, reptiles, birds, and mammals. They
range in size from some fishes only an inch long as adults to the blue whale. General Characteristics:
All chordates have a dorsal hollow nerve tube, a notochord, and pharyngeal gill
slits. All vertebrates (members of a subphylum of chordata) have a backbone
(spinal column) and a closed circulatory system.Geographic Range:
Vertebrates are found worldwide, except at the very centers of the polar ice
caps.Habitat:
Vertebrates occur in essentially every habitat on Earth, including the open
ocean, the deepest sea bottoms, the air, and the edges of the polar ice caps.
They may be marine, freshwater, terrestrial, aerial, or subterranean.Food Web:
Vertebrates feed on essentially every available source of food. They may be
herbivores, carnivores, or omnivores.Reproduction and
Development:
Vertebrates display an amazing range of reproductive adaptations. Some Species lay eggs,
while others bear live young. The live young may be nourished by the mother (as
in mammals) or simply develop as eggs within the mother's body (as in
rattlesnakes). Vertebrates may build a nest and care for the young to varying degrees,
or they may simply release their gametes into the environment to develop
without help from the parents. Most Species of
vertebrate participate in sexual reproduction, but some Speces of fishes and reptiles are all female and do not undergo
sexual reproduction.

ORGANISIMSFrog (Amphibias)
Reproduction:
Mating for amphibians must nearly always occur in fresh water. It consists of
the joining of the male and female frog, and at this time, the female lays eggs
while the male releases sperm. The fertilized eggs are now left alone by both
parents. The young that hatch will survive on their own. Amphibian eggs are
protected by a jelly-like substance before hatching, unlike the hard or
semi-hard shells of reptiles and birds.Lizard (Reptilias)
Reproduction:
In reptiles, egg fertilization occurs internally when the male places his sperm
inside eggs within the female's body. The male does this by inserting his penis
into the female cloaca. In many species, this sperm can remain intact for years
so the female can produce additional offspring without any other male contact.
Interestingly, some species of lizards actually produce offspring without males
in a process known as parthenogenesis.Flagfish (Fish)
Reproduction:
When an egg-laden female comes by, they do a rough courtship dance that looks
like a milder version of fighting. Then, the male curves over the female in a
horsehoe-shape. As the female releases her eggs, the male immediately
fertilizes them. The female lays an average of 350 eggs, but usually not all of
them will survive. The female will drift as if stunned, while the male places
the fertilized eggs in each of the bubbles of the bubblenest. They can repeat
all of this for up to one day.